1. Field of the Invention
The present invention relates to data communication devices, and more particularly to portable connection circuits emulating a telephone network for conforming a facsimile device into a local printer or scanner.
2. Description of the Prior Art
The current development explosion in solid state technology, particularly in the processing rate and density of a microprocessor, along with parallel advances in memory devices, have now resulted in data processing systems that are fully compatible with a user. Simply, the evolution of these fundamental components is now at a capacity sufficient to handle high quality operating systems, and the resulting combination is now wholly `user friendly` in all its domesticated forms. Laptop computers, palm-sized computers, and those even smaller are therefore now part of the landscape.
While the processing facility is now reaching the acceptance (and dimensions) of a pocket calculator, the physical dimensions of printing still limit the portability aspects of word processing systems.
Coincidentally, however, a concurrent evolution occurred in telephone transmission of image facsimilies. A facsimile device, with its print mechanism, is now part of any office, hotel facility, or other commercial establishment, and is proliferating with increasing frequency even in homes. The print mechanisms of a facsimile device are therefore now widely distributed in their various forms.
Telephonic transmission of images is constrained to the bandwidth of the telephone network, and the cost of transmission is a significant component of the design and selection of the device. As result the many compromises between print fidelity, the cost of telephone time and device complexity have evolved various commercial forms, and a wide variety of facsimile devices are now in the marketplace.
Each facsimile device, however, is physically limited, or fixed, by the limitations of the telephone network to a standardized communication format and therefore includes extensive logic in its operating system to determine the characteristics of the connecting device. Thus elaborate `handshake` protocols are exchanged at the start of transmission which are then automatically processed as a part of the operating system through a communication interface with the telephone network, referred to as the modulator/demodulator (modem). As the evolution in data processing progressed, the function of this operating system that is tied to the modem has expanded, and now includes automatic dialing and other functions that remove and isolate the user from the mechanics of telephone line connection. Simply, to the user these functions are now virtually invisible, and a `user-friendly` device only asks of the user to key in the destination telephone number and takes over from there.
The same user friendly aspects are now installed in the fax-modem of the computer. Thus little external control is available at both ends of a computer-facsimile combination over the TIP and RING functions of the telephone network. Like described above, the computer, provided with a fax-modem, automatically dials (and sometime re-dials) the destination number, discerns the line connection and generates and inspects the respective handshake signals, all without any participation by the user. As these `user friendly` features of the system increase, less and less flexibility is available over this interconnection. Simply, the operating system controlling both modem interfaces is directed to the functions of a telephone network, and any mechanism for direct connection is best effected by emulation thereof.
In the past various techniques have been devised which allow for local connection of a facsimile device to a processor, to effect the functions of a printer. Examples of such techniques may be found in U.S. Pat. Nos. 5,530,558 to Nachman; 4,991,200 to Lin; and 5,528,385 to Manning. While suitable for the purposes intended, each of the foregoing impose on the user steps of manual intervention which are often improperly effected and more recently not compatible with the automatic dialing imbedded in current `user-friendly` systems.
Commercial devices, like those sold under the Model No. DLE-200B by VIKING ELECTRONICS, INC., Hudson, Wis., similarly require selective articulation of manual switches, like the START switch on the facsimile assembly, along with operational modes that omit the dialing sequence. At the other extreme commercial devices, like those sold under the mark or style MISSING LINK, by BROTHER INTERNATIONAL CORP., Somerset, N.J., attempt to resolve the above problem by logical sequences, but in a manner requiring multi-pin connection ports, high processing rates, and high capacity storage. Thus, while suitable for the purposes intended, the commercially available devices fail to address the simplified user involvement in current data processing tasks, in an assembly that is both reliable and inexpensive in manufacture. A simple and inexpensive interconnection system that passively emulates the dialing responses of a telephone network is therefore desired and it is one such system that is disclosed herein.